Hollis, 32, was shot in the head on June 24 during a fight between two groups, which police attempted to break up. Police say Hollis was working an off-duty shift in full uniform. The shooting occurred shortly after the Jazz in the Park concert series ended around 8 p.m. at City Park.

Before Hollis died, she had been working to set up a bone-marrow drive for a Colorado Army National Guardsman.

On Friday, her fellow officers and friends will make sure that event goes on as planned. The bone-marrow drive will take place from 11 a.m. until 2 p.m. at Denver Police District 2 on Holly Street. The test only takes 15 minutes and is just a cheek swab.

Police arrested 21-year-old Rollin Oliver on suspicion of the murder of Hollis. He is charged with first-degree murder with extreme indifference.

Jail records reviewed by the 9Wants To Know and The Denver Post show Oliver claimed he was a member of the Park Hill Bloods gang.

Investigators are urging eyewitnesses or anyone with information to contact Denver Metro Crime Stoppers at 720-913-STOP (7867.) They particularly want any photos of the crowd.